Small bowel hydro-MR imaging for optimized ileocecal distension in Crohn's disease: should an additional rectal enema filling be performed?

PURPOSE: To assess the impact of an additional rectal enema filling in small bowel hydro-MRI in patients with Crohn's disease. MATERIALS AND METHODS: A total of 40 patients with known Crohn's disease were analyzed retrospectively: 20 patients only ingested an oral contrast agent (group A), the other 20 subjects obtained an additional rectal water enema (group B). For small bowel distension, a solution containing 0.2% locust bean gum (LBG) and 2.5% mannitol was used. In all patients, a breathhold contrast-enhanced T1w three-dimensional volumetric interpolated breathhold examination (VIBE) sequence was acquired. Comparative analysis was based on image quality and bowel distension as well as signal-to-noise ratio (SNR) measurements. MR findings were compared with those of conventional colonoscopy, as available (N = 25). RESULTS: The terminal ileum and rectum showed a significantly higher distension following the rectal administration of water. Furthermore, fewer artifacts were seen within group B. This resulted in a higher reader confidence for the diagnosis of bowel disease, not only in the colon, but also in the ileocecal region. Diagnostic accuracy in diagnosing inflammation of the terminal ileum was 100% in group B; in the nonenema group there were three false-negative diagnoses of terminal ileitis. CONCLUSION: Our data show that the additional administration of a rectal enema is useful in small bowel MRI for the visualization of the terminal ileum. The additional time needed for the enema administration was minimal, and small and large bowel pathologies could be diagnosed with high accuracy. Thus, we suggest that a rectal enema in small bowel MR imaging be considered.

Dark lumen magnetic resonance colonography in a rodent polyp model: initial experience and demonstration of feasibility.

PURPOSE: We sought to assess dark lumen magnetic resonance (MR) colonography for the detection of colon polyps in a rodent model with histology as the gold standard. MATERIAL AND METHODS: Fourteen male Wistar rats were subjected to carcinogenic N-methyl-N'-nitro-N-nitrosoguanidine at the age of 4 months to induce colon neoplasms. MR imaging was performed after a time interval of 1 year. Preparation and data acquisition was performed with the animals under full anesthesia. After a body-warm saline enema images were acquired on a clinical 1.5-T whole-body MR system using a standard extremity coil. Plain and contrast-enhanced (0.3 mmol/kg; Gd-DOTA; Dotarem, Guerbet, France) 3-dimensional T1-weighted gradient recall echo images were acquired. Two radiologists analyzed the MR data sets in consensus for lesion depiction. Contrast uptake in colonic wall and polyps was quantitatively assessed by signal-to-noise ratio and contrast-to-noise ratio measurements and compared using a Wilcoxon-Mann-Whitney U test with statistical significance at a P value < 0.05. Finally, all animals were killed, and the MR imaging results were compared with pathologic findings. Sensitivity and specificity were calculated. RESULTS: By pathology, a total of 15 polyps were found in 9 of 14 rats. MR colonography detected 13 of 15 polyps measuring between 4 and 11 mm (mean 7 +/- 0.6 mm) in 8 of 9 animals, resulting in a sensitivity and specificity of 0.87 and 1.0, respectively. Compared with the precontrast data, all polyps showed a statistically significant increase in signal-to-noise ratio (78.2 +/- 6.3 to 167.4 +/- 17.7) and contrast-to-noise ratio (45.4 +/- 5.2 to 124.6 +/- 11.2). CONCLUSION: MR colonography with a dark colon lumen and a bright, contrast-enhanced colon wall appears well suited for the detection of colonic lesions in a rodent model.